1. Field of the Invention
The present invention relates, in general, to flat fluorescent lamps and backlight units using the same, and more specifically, to a flat fluorescent lamp having an electrode structure to cause a dielectric barrier discharge, and a backlight unit using the same.
2. Description of the Related Art
In general, a flat display device is classified into a light-emitting type and a light-receiving type, in which the light-emitting type display device includes a cathode ray tube, an electron light-emitting device, a plasma display panel, etc., and the light-receiving type display device is exemplified by a liquid crystal display.
However, the liquid crystal display per se has no a light-emitting structure, and cannot display an image unless light is externally irradiated. Thus, an additional light source, for example, a backlight unit, is mounted to display the image.
Such a backlight unit acts to diffuse light irradiated from a cold cathode fluorescent lamp (CCFL) through a light plate and a diffusion plate, or may diffuse light by exciting a fluorescent material through ultraviolet rays by use of a flat fluorescent lamp.
With reference to FIG. 1, there is shown a conventional flat fluorescent lamp. Such a fluorescent lamp 10 includes a back substrate 11, and a front substrate 12 mounted at predetermined intervals to the back substrate 11 through a sealing member 13, whereby a discharge channel is formed between the back and front substrates 11 and 12. In addition, a fluorescent material layer 16 is formed to a bottom surface of the front substrate 12, and discharge electrodes 14 are formed in a predetermined pattern to a top surface of the back substrate 11 corresponding to the fluorescent material layer 16. Further, a dielectric layer 15 is formed on the back substrate 11 to embed the discharge electrodes 14 therein. In the discharge channel, a discharge gas, such as xenon (Xe), neon (Ne), etc., is filled.
The conventional flat fluorescent lamp 10 is structured to cause a surface light emission by exciting the fluorescent material layer 16 through ultraviolet rays generated by a surface discharge of the electrodes, according to the application of a power to the discharge electrodes 14.
However, since the conventional flat fluorescent lamp mainly employs an inert gas, such as xenon (Xe), neon (Ne) or Xe—Ne, as a discharge gas, it has an alternating voltage as high as 2 kV that is applied to the discharge electrodes 14, and a light efficiency as low as 30 lm/W or less. Hence, with the intention of obtaining large quantities of light, the discharge channel of the above lamp 10 should be enlarged and an operation power should increase, resulting in increased power consumption. In addition, since the used discharge gas is inert, the fluorescent material layer 16 is excited by ultraviolet rays of 147 or 173 μm. Consequently, the above fluorescent lamp is disadvantageous in terms of using an expensive fluorescent material, instead of a mass-produced fluorescent material for ultraviolet rays of 254 μm.
On the other hand, a typical flat fluorescent lamp using mercury has a long serpentine type discharge channel, in which electrodes are disposed to a staring point and an ending point of the discharge channel. Thereby, relatively large electrical current flows in the discharge channel, and mercury can be easily evaporated, thus realizing the high efficiency of a mercury discharge.
However, as the discharge channel becomes longer, a voltage required to initiate the discharge increases. In cases of increasing the discharge voltage, the lamp may suffer from unstability, current leakage and electronic wave problems. Further, a flat fluorescent lamp is large-sized in recent years, due to the use of a large liquid crystal display, whereby there is necessary a drastically lengthened serpentine channel. Hence, it is impossible to realize a circuit required for such a discharge voltage.
To solve the problems, Korean Patent Laid-open Publication No. 2001-0079377 discloses a flat fluorescent lamp and a manufacturing method thereof.
The disclosed manufacturing method of the flat fluorescent lamp includes heating a flat glass plate to predetermined molding temperatures, molding the heated flat glass plate by use of a mold processed to have a plurality of discharge channels separated by partitions and communicated with discharge paths, to prepare a molded flat glass plate having discharge channels, removing the molded glass plate from the mold, slowly cooling the molded glass plate, coating a fluorescent material to the insides of the discharge channels of the molded glass plate, followed by a burning process, attaching the glass plate to a front cover through a seal paste, removing air from the insides of the discharge channels of the glass plate, introducing a discharge gas into the discharge channels, sealing exhaust ports of the discharge channels, and mounting electrodes to apply high frequency power to the discharge channels.
As for the above method, the electrodes used for the application of the high frequency power are inner electrodes mounted to the insides of the discharge channels or are disposed along the entire longitudinal lengths of both lateral surfaces of the discharge channels.
Although such a flat fluorescent lamp is difficult to fabricate because of molding the heated glass plate to define the discharge channels, it has no problems related to the application of the high voltage to the electrodes. However, crosstalk between the discharge channels may occur, due to a strong discharge in a specific discharge channel among the discharge channels or severely shaking discharge plasma.
This is because discharge charges are easily moved through the inner surfaces of apertures of the electrodes and thus the discharge charges crowd in the discharge channel which relatively easily causes the discharge.
Japanese Patent Laid-open Publication No. Sho. 60-216435 discloses a flat fluorescent lamp, in which partitions are alternately disposed in a zigzag shape in a chamber having a closed space to define a serpentine discharge channel. Further, electrodes are disposed to both ends of the discharge channel, and fluorescent material layers are formed on the top and bottom of the discharge channels. However, such a flat fluorescent lamp suffers from drawbacks, such as non-uniform luminance, due to weak light emission at an edge of the discharge channel, requirement of a high discharge voltage, and easy deterioration of the electrodes.
In Japanese Patent Laid-open Publication No. Hei. 09-092208 and U.S. Pat. Nos. 5,903,096 and 5,509,841, there is disclosed a planar light source having a serpentine channel defined by partitions. In particular, U.S. Pat. No. 5,509,841 discloses a metallic body having a serpentine channel.